Need help with semi truck gear ratios and front wheels

[novaris]

I'm converting my scania r470 to a 4x4 and running it off road (sandy, grass)
I plan to get a compact single speed transmission since the size of the stock transmission it makes it difficult to fit u joints

1. So i hope someone can illustrate how fast can it go on the 3 gears so i would know which the pinion gear to get if i want to as fast as a ta01 hummer on stock motor and gear

2. Where can i find suitably sized hex wheels for the front axles apart from the rear inner wheels?